/Engine/Plugins/Interchange/Runtime/Source/Import/Public/Fbx/InterchangeFbxTranslator.h
Release source is called when we do not need anymore the translator source and also early in the cancel process. This is where out of process translator will send the stop command. A good example of why its useful to release the source is when the dispatcher delete the worker, the join on the thread will be very short and will not block the main thread. If the worker stop command was send before the completion task.
virtual void ReleaseSource()